1. Field of the Invention
The present invention relates to a semiconductor laser and, more particularly, to a structure of a semiconductor laser using a p-type InP substrate.
2. Background Art
Semiconductor materials from such systems as an InGaAsP system and an AlGaInAs system are used for a material of a semiconductor laser for use in communication with a 1.3 μm band and a 1.55 μm band. These materials have bandgap energies corresponding to the above-mentioned wavelength range and can be lattice-matched to the InP of the substrate. Moreover, as a substrate of the above-mentioned semiconductor laser, a p-type substrate is in wide use. This is because an NPN type bipolar transistor operable at a high speed can be used as a driving circuit.
FIG. 7 is a cross-sectional view illustrating a conventional InGaAsP system semiconductor laser element formed by employing a p-type substrate.
This semiconductor laser is produced by using a p-type substrate 1 containing Zn. A Zn-doped p-type InP clad layer 4, an InGaAsP optical confinement layer 5, an InGaAsP MQW (Multiple Quantum Well) 6, an n-type InGaAsP optical confinement layer 7, and an n-type InP clad layer 8 are successively stacked on the p-type substrate 1 to be formed in a film. This stacked film has slopes on both sides thereof. A p-type InP buried layer 10, an n-type InP current blocking layer 11, and a p-type current blocking layer 12 are provided outside these slopes. Moreover, an n-type InP contact layer 13 is formed on the n-type InP clad layer 8 and the p-type current blocking layer 12 so as to cover the entire area of both layers (for example, it should be referred to Japanese Unexamined Patent Publication No. 2001-53385).